Ionization Chamber Having a Potential-Well for Ion Trapping and Ion Compression

ABSTRACT

An ionization chamber. The ionization chamber includes a vessel, an ionization source, an ion gate, and a mid-ring electrode. The vessel defines an ionization region. The vessel includes a first end axially disposed opposite a second end. The ionization source is located at the first end and generates ions. The ion gate is located at the second end of the vessel. The mid-ring electrode is located between the ionization source and the ion gate. During an ion compression stage, the ionization source is charged to a first ionization source potential, the ion gate is charged to a first ion gate potential, and the mid-ring electrode is charged to a first mid-ring potential that is less than the first ionization source potential and the first ion gate potential. The first mid-ring potential is configured to generate a potential well proximate the mid-ring electrode. The ions collect at the potential well.

PRIORITY

This application is a continuation application of U.S. patentapplication Ser. No. 15/820,331, entitled “IONIZATION CHAMBER HAVING APOTENTIAL-WELL FOR ION TRAPPING AND ION COMPRESSION” and filed on Nov.21, 2017, which claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/439,580, of the same title and filed on Dec.28, 2016, both of which are hereby incorporated by reference herein intheir entirety.

BACKGROUND

The field of the disclosure relates generally to ion mobilityspectrometer (IMS) systems and, more particularly, to an ionizationchamber having a potential-well for ion trapping and ion compression.

At least other some known spectrometry detection devices include ionmobility spectrometer (IMS), such as, for example, an ion trap mobilityspectrometer (ITMS). Many of the known ITMS detection systems include acollection device that collects particulate, liquid, and/or gaseoussamples from an object of interest. The samples are channeled to anionization chamber that includes an ionizing source that ionizes thesample to form positive ions, negative ions, and free electrons. Theionization chamber in ITMS detection systems is typically a field-freeregion. As the ions are generated in the ionization chamber to increasethe ion population therein, a retaining grid, or gate, is maintained ata slightly greater potential than the electric field in the ionizationchamber to induce a retention field and reduce the potential for ionleakage from the chamber. Thus, the ions are “trapped” within theionization chamber or ionization region. An electric field is theninduced across the ionization chamber and, depending on the polarity ofthe induced electric field, the positive ions or the negative ions arepulsed from the ionization chamber, through a high-voltage “kickoutpulse,” into a drift region through the retaining grid. The ions of theopposite polarity are attracted to the walls of the ionization chamberand are discharged there.

In some ITMS detection systems, the drift region includes a plurality ofsequential, annular electrodes. A collector electrode is positioned onthe opposite side of the drift region from the ionization chamber and isheld at a ground potential. For those systems that use negative ions,the annular electrodes are energized to voltages that are sequentiallyless negative between the ionization chamber and the collectorelectrode, thereby inducing a constant positive field. Motion is inducedin the negative ions from the initial pulse in the ionization chamberand the ions are channeled through the drift region to the collectorelectrode. Signals representative of the ion population at the collectorelectrode are generated and transmitted to an analysis system todetermine the constituents in the collected samples.

The population of ions is pulsed into the drift region from theionization chamber typically in the form of an ion disk with apredetermined axial width value and possibly a trailing ion tail. As thedisk of ions traverses the drift region, high-mobility analytes separatefrom low-mobility analytes induces expansion and distortion of the iondisk. The high-mobility analytes form a disk that transits faster than adisk formed of low-mobility analytes and the disks may overlap as theyare received at the collector electrode. The peaks on the trace thusgenerated on the spectral analysis equipment are distorted with poorresolution and are difficult to analyze. Moreover, in many ITMSdetection systems, there is no precise control over the width of the iondisk injected into the drift region. Fundamentally, this is due toinconsistent, and sometimes, incomplete clearing out of the ionizationchamber due to non-homogeneity of the electric field induced in theionization chamber, e.g., low field regions at the back of theionization chamber.

SUMMARY

In one aspect, an ionization chamber is provided. The ionization chamberincludes a vessel, an ionization source, an ion gate, and a mid-ringelectrode. The vessel defines an ionization region. The vessel includesa first end axially disposed opposite a second end. The ionizationsource is located at the first end and generates ions. The ion gate islocated at the second end of the vessel. The mid-ring electrode islocated between the ionization source and the ion gate. During an ioncompression stage, the ionization source is charged to a firstionization source potential, the ion gate is charged to a first ion gatepotential, and the mid-ring electrode is charged to a first mid-ringpotential that is less than the first ionization source potential andthe first ion gate potential. The first mid-ring potential is configuredto generate a potential well proximate the mid-ring electrode. The ionscollect at the potential well.

Optionally, said ion gate is further configured to be charged to thefirst ion gate potential to prevent the ions from traveling through saidion gate and from said vessel.

Optionally, said ionization source is further configured to be chargedto the first ionization source potential to evacuate the ions from thefirst end of said vessel.

Optionally, the first ionization source potential is equal to the firstion gate potential.

Optionally, during a release stage: said ionization source is furtherconfigured to be charged to a second ionization source potential that isgreater than the first ionization source potential; said mid-ringelectrode is further configured to be charged to a second mid-ringpotential that is greater than the first mid-ring potential; and saidion gate further configured to be charged to a second ion gate potentialthat is less than the second mid-ring potential and the secondionization source potential, wherein the second mid-ring potential andthe second ion gate potential are configured to cooperate to move apulse of the ions through said ion gate and from said second end of saidvessel. Optionally, during the release stage, a difference between thesecond ionization source potential and the second mid-ring potential isless than a difference between the second mid-ring potential and thesecond ion gate potential.

Optionally, said mid-ring electrode is further configured to be chargedto a potential gradient over an axial dimension of said mid-ringelectrode. Optionally, the potential gradient is axially asymmetrical.

Optionally, said ion gate comprises a conductive grid disposed betweenthe ionization region and a drift region.

In another aspect, a method of compressing ions is provided. The methodincludes generating ions at an ionization source within an ionizationchamber. The method includes charging a mid-ring electrode to a firstmid-ring potential to generate a potential well relative to a firstionization source potential and a first ion gate potential, thepotential well configured to collect the ions. The method includescharging an ion gate to the first ion gate potential to prevent the ionsfrom traveling through the ion gate and into a drift region.

Optionally, the method further comprises charging the ionization sourceto the first ionization source potential, wherein the first ionizationsource potential and the first ion gate potential are greater than thefirst mid-ring potential. Optionally, the method further comprises:charging the mid-ring electrode to a second mid-ring potential that isgreater than the first mid-ring potential; and charging the ion gate toa second ion gate potential that is less than the second ionizationsource potential and the second mid-ring potential to pulse the ionsinto the drift region. Optionally, the second ion gate potential isequal to the first ion gate potential. Optionally, the second ionizationsource potential and the second mid-ring potential are greater than thesecond ion gate potential, such that a pulse of the ions travel throughthe ion gate.

Optionally, charging the mid-ring electrode to the first mid-ringpotential comprises charging the mid-ring electrode with a potentialgradient over a length of the mid-ring electrode in an axial dimensionof the ionization chamber.

In yet another aspect, an ion mobility spectrometer (IMS) device isprovided. The IMS device includes a drift tube and an ionizationchamber. The ionization chamber includes an ionization source, an iongate, and a mid-ring electrode. The drift tube defines a drift regiontherein. The ionization chamber defines an ionization region therein.The ionization source is located at a first end of the ionization regionand is configured to generate ions. The ionization source is configuredto be charged to a first ionization source potential during an ioncompression stage. The ion gate is located adjacent to the drift tubeand at a second end of the ionization region. The ion gate is configuredto be charged to a first ion gate potential during the ion compressionstage. The mid-ring electrode is located between the ionization sourceand the ion gate. The mid-ring electrode is configured to be charged,during the ion compression stage, to a first mid-ring potential that isless than the first ionization source potential and the first ion gatepotential. The first mid-ring potential is configured to generate apotential well, proximate the mid-ring electrode, where the ions collectduring the ion compression stage.

Optionally, during a release stage: said ionization source is furtherconfigured to be charged to a second ionization source potential that isgreater than the first ionization source potential; said mid-ringelectrode is further configured to be charged to a second mid-ringpotential that is greater than the first mid-ring potential; and saidion gate is further configured to be charged to a second ion gatepotential that is less than the second ionization source potential andthe second mid-ring potential, wherein the second ionization sourcepotential, the second mid-ring potential, and the second ion gatepotential are configured to cooperate to move a pulse of the ionsthrough said ion gate and into said drift region.

Optionally, during the release stage, a difference between the secondionization source potential and the second mid-ring potential is lessthan a difference between the second mid-ring potential and the secondion gate potential.

Optionally, said mid-ring electrode is further configured to be chargedto a potential gradient over an axial dimension of said mid-ringelectrode.

Optionally, said ion gate is further configured to be charged to thefirst ion gate potential to prevent the ions from traveling through saidion gate and into said drift region.

Optionally, said ionization source is further configured to be chargedto the first ionization source potential to evacuate the ions from thefirst end of said ionization region.

Optionally, said ion gate comprises a Bradbury-Nielson gate.

The aforementioned and other embodiments of the present specificationshall be described in greater depth in the drawings and detaileddescription provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a perspective diagram of an exemplary ion mobilityspectrometry device;

FIG. 2 is a cross-sectional diagram of the ion mobility spectrometrydevice shown in FIG. 1;

FIG. 3 is a potential diagram of the ionization chamber shown in FIGS. 1and 2 during a compression stage;

FIG. 4 is a potential diagram of the ionization chamber shown in FIGS. 1and 2 during a release stage; and

FIG. 5 is a flow diagram of an exemplary method of compressing ions inthe ionization chamber shown in FIGS. 1 and 2.

Unless otherwise indicated, the drawings provided herein are meant toillustrate features of embodiments of this disclosure. These featuresare believed to be applicable in a wide variety of systems comprisingone or more embodiments of this disclosure. As such, the drawings arenot meant to include all conventional features known by those ofordinary skill in the art to be required for the practice of theembodiments disclosed herein.

DETAILED DESCRIPTION

In the following specification and the claims, a number of terms arereferenced that have the following meanings.

The singular forms “a”, “an”, and “the” include plural references unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, “approximately”, and “substantially”, are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged. Such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.

The present specification is directed towards multiple embodiments. Thefollowing disclosure is provided in order to enable a person havingordinary skill in the art to practice the invention. Language used inthis specification should not be interpreted as a general disavowal ofany one specific embodiment or used to limit the claims beyond themeaning of the terms used therein. The general principles defined hereinmay be applied to other embodiments and applications without departingfrom the spirit and scope of the invention. Also, the terminology andphraseology used is for the purpose of describing exemplary embodimentsand should not be considered limiting. Thus, the present invention is tobe accorded the widest scope encompassing numerous alternatives,modifications and equivalents consistent with the principles andfeatures disclosed. For purpose of clarity, details relating totechnical material that is known in the technical fields related to theinvention have not been described in detail so as not to unnecessarilyobscure the present invention.

In the description and claims of the application, each of the words“comprise” “include” and “have”, and forms thereof, are not necessarilylimited to members in a list with which the words may be associated. Itshould be noted herein that any feature or component described inassociation with a specific embodiment may be used and implemented withany other embodiment unless clearly indicated otherwise.

Embodiments of the IMS systems described herein provide an ionizationchamber having one or more mid-ring electrodes. More specifically, themid-ring electrode is charged to a low potential to generate a potentialwell within the ionization chamber. The potential well operates tocollect ions during a compression stage such that, during a releasestage, a higher-density pulse of ions is released into a drift region inwhich detection is carried out. The potential well is further configuredto be charged relative to a potential of the ionization source and apotential of the ion gate. The potentials of the ionization source,mid-ring electrode, and the ion gate cooperate to move ions away fromthe ionization source during compression and release. The potentials ofthe ionization source, mid-ring electrode, and the ion gate furthercooperate to collect the ions near the ion gate in a higher-density thanin a field-free ionization region. The potentials of the mid-ringelectrode and the ion gate are configured to increase the density ofions during compression without allowing ions to travel through the iongate into the drift region. The increased density of ions results in ahigh-density pulse of ions released into the drift region, thusincreasing the ion signal and improving detection performance.

FIG. 1 is a perspective diagram of an exemplary IMS device 100. IMSdevice 100 includes an ionization chamber 102, within which anionization region 104 is defined, coupled to a drift tube 106, withinwhich a drift region 108 is defined. Ionization chamber 102 generallyincludes a vessel within which an ionization source 110 is located, at afirst end of ionization chamber 102, and within which an ion gate 112 islocated, at a second end of ionization chamber 102. Ionization chamber102 includes a mid-ring electrode 114 located between ionization source110 and ion gate 112.

During a compression stage, ionization source 110 generates ions 116that are mixed with a sample 118 that is injected into ionizationchamber 102. During a release stage, a pulse of ions 120 is releasedthrough ion gate 112 and into drift region 108.

Ion gate 112, in certain embodiments, includes a conductive grid or meshmaterial that is charged as an electrode. Such an embodiment having aconductive grid is referred to as an ion trap mobility spectrometer(ITMS) device. In alternative embodiments, ion gate 112 includes aBradbury-Nielson gate. The Bradbury-Nielson gate includes two sets ofalternating wires that are charged to an equal potential during therelease stage. The potential of the two sets of alternating wires isless than the potential of ionization source 110 and higher than thepotential of drift region 104 during the release stage. During ioncompression, the potential of one set of alternating wires is offsetrelative to the potential of the second set of alternating wires. Suchpotentials prevent ions near the gate from traveling through ion gate112 and into drift region 104 by causing the ions to collide with thesets of alternating wires. During the ion compression stage, the firstmid-ring potential is less than the first ionization source potentialand the first ion gate two wires' potential.

FIG. 2 is a cross-sectional diagram of ITMS device 100, shown in FIG. 1.FIG. 2 illustrates ionization chamber 102 and drift region 108. Duringthe compression stage, ions 116 are generated by ionization source 110and mixed with sample 118 in ionization region 104. Mid-ring electrode114 is charged to a lower potential than ionization source 110 and iongate 112 to generate a potential well within ionization region 104. Ions116 collect in the potential wells in a narrow band near ion gate 112.During the release stage, pulse 120 of ions 116 travels through ion gate112 and into drift region 108.

Drift tube 106 includes a series of electrodes 202, 204, 206, 208, 210,and 212 axially disposed along the length of drift tube 106. Electrodes202, 204, 206, 208, 210, and 212 are charged to respective potentials togenerate a flow of pulse 120 of ions 116 from ion gate 112 through driftregion 108.

FIGS. 3 and 4 are potential diagrams of ionization chamber 102, shown inFIGS. 1 and 2. FIG. 3 is a potential diagram during the compressionstage, and FIG. 4 is a potential diagram during the release stage. Thepotential diagrams of FIGS. 3 and 4 illustrate potentials at ionizationsource 110, ion gate 112, mid-ring electrode 114, and drift region 108.

Referring to FIG. 3, mid-ring electrode 114 is charged to be at a lowerpotential than ionization source 110 and ion gate 112. The low potentialof mid-ring electrode 114 generates a potential well 302 in whichgenerated ions collect. More specifically, the potential of ionizationsource 110 relative to potential well 302 results in ions moving awayfrom ionization source 110 toward ion gate 112. The potential of iongate 112 relative to potential well 302 results in the ions collectingnear ion gate 112, but far enough from ion gate 112 that ions do nottravel, or “leak,” through ion gate 112 into drift region 108. Thepotential difference between potential well 302 and ionization source110 and the potential difference between potential well 302 and ion gate112 may range from ten volts to several hundred volts, depending on thespecific implementation. Generally, as the depth of potential well 302increases, the so too does the ion concentration. However, thepotentials at which ionization source 110, ion gate 112, and mid-ringelectrode 114 are charged should be optimized to achieve a highconcentration of ions in potential well 302 while still ensuring theions have sufficient energy to be “kicked out” of potential well 302during the release stage. Moreover, the potentials of ionization source110 relative to ion gate 112 may be equal or offset, depending on thespecific implementation. In certain embodiments, the potential ofmid-ring electrode 114 is maintained at a potential gradient along theaxial dimension of ionization region 104. The potential gradient, incertain embodiments, is symmetrical in the axial dimension, for example,forming a potential trough at an axial mid-point of potential well 302.In other embodiments, the potential gradient is asymmetrical in theaxial dimension, for example, forming a potential trough nearer ion gate112 relative to the axial mid-point. Potential well 302 collects ahigh-density population of ions near ion gate 112. In such embodiments,mid-ring electrode 114 may be composed of a semiconductor material tocontrol the potential gradient.

Referring to FIG. 4, which illustrates potentials of ionization chamber102 during the release stage, ionization source 110 and mid-ringelectrode 114 are charged to a higher potential than ion gate 112 anddrift region 108. In certain embodiments, potentials of ionizationsource 110 and mid-ring electrode are equal or offset with respect toeach other, while still at a higher potential than ion gate 112. Incertain embodiments, the potential of ion gate 112 is equal during boththe compression stage and the release stage. Generally, such potentialenable a pulse of ions to move from ionization chamber 104, through iongate 112, and into drift region 108. The release of a pulse of ionsthrough ion gate 112 is enabled by lowering the potential of ion gate112, or “pulsing” ion gate 112, for a pulse duration, after which thepotential of ion gate 112 is increased to resume trapping ions inionization region 104. The potential of ionization source 110, incertain embodiments, is greater than the potential of mid-ring electrode114. In alternative embodiments, ionization source 110 and mid-ringelectrode 114 are charged to an equal potential or slightly offset. Forexample, ionization source 110 may be offset by plus-or-minus 10 voltsrelative to mid-ring electrode 114. Such offset, or the potentialdifference between ionization source 110 and mid-ring electrode 114, isless than the potential difference between mid-ring electrode 114 andion gate 112. Such potentials ensure ions move from ionization region104 into drift region 108 during the release stage.

Referring again to FIGS. 3 and 4, the high-density population of ions inpotential well 302 during the compression stage enables a highconcentration of ions to pulse through ion gate 112 during the releasestage. Thus, a high-density pulse of ions travels from ion gate 112 andthrough drift region 108, improving the ion signal and further improvingdetection performance.

FIG. 5 is a flow diagram of an exemplary method 500 of compressing ionsionization chamber 102, shown in FIGS. 1 and 2. Method 500 begins at astart step 510. Method 500 includes generating 520 ions 116 usingionization source 110 within ionization chamber 102. Mid-ring electrode114 is charged 530 to a first mid-ring potential to generate potentialwell 302 relative to a first ionization source potential of ionizationsource 110 and a first ion gate potential of ion gate 112. Potentialwell 302 is configured to collect ions 116. Ion gate 112 is charged 540to the first ion gate potential to prevent ions 116 from travelingthrough ion gate 112 and into drift region 108.

In certain embodiments, during the compression stage, ionization source110 is charged to the first ionization source potential, where the firstionization source potential and the first ion gate potential are greaterthan the first mid-ring potential. Further, in certain embodiments,during the release stage, mid-ring electrode 114 is charged to a secondmid-ring potential that is greater than the first mid-ring potential.Also during the release stage, ion gate 112 is charged to a second iongate potential that is less than the first ion gate potential to pulseions 116 into drift region 108. Method 500 terminates at an end step550.

An exemplary technical effect of the methods, systems, and apparatusdescribed herein includes at least one of: (a) generating a potentialwell into which ions collect before being pulsed into a drift region;(b) increasing an ion density in the potential well region duringcompression and in the pulse during release; (c) improving ion signalintensity for the pulse of ions during detection; (d) charging amid-ring electrode within the ionization chamber with a potentialgradient; (e) charging the ionization source, the mid-ring electrode,and the ion gate during compression to move ions away from theionization source; (f) charging the ionization source, the mid-ringelectrode, and the ion gate during compression to move ions toward theion gate; and (g) charging the mid-ring electrode and the ion gateduring compression to prevent ions from traveling through the ion gate.

Exemplary embodiments of methods, systems, and apparatus for dual sourceionizers are not limited to the specific embodiments described herein,but rather, components of systems and/or steps of the methods may beutilized independently and separately from other components and/or stepsdescribed herein. For example, the methods may also be used incombination with other non-conventional ion trap mobility spectrometers,and are not limited to practice with only the systems and methods asdescribed herein. Rather, the exemplary embodiment can be implementedand utilized in connection with many other applications, equipment, andsystems that may benefit from increased efficiency, reduced operationalcost, and reduced capital expenditure.

Although specific features of various embodiments of the disclosure maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the disclosure, any featureof a drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

What is claimed is:
 1. An ionization chamber, comprising: a vesselwithin which an ionization region is defined, said vessel comprising afirst end axially disposed opposite a second end; an ionization sourcelocated at said vessel's first end and configured to generate ions, saidionization source configured to be charged to a first ionization sourcepotential during an ion compression stage; an ion gate located at saidsecond end and configured to be charged to a first ion gate potentialduring the ion compression stage; and a mid-ring electrode locatedbetween said ionization source and said ion gate, said mid-ringelectrode configured to be charged, during the ion compression stage, toa first mid-ring potential that is less than the first source potentialand the first ion gate potential, the first mid-ring potentialconfigured to generate a potential well, proximate said mid-ringelectrode.
 2. The ionization chamber of claim 1, wherein said ion gateis further configured to be charged to the first ion gate potential toprevent the ions from traveling through said ion gate and from saidvessel.
 3. The ionization chamber of claim 1, wherein said ionizationsource is further configured to be charged to the first ionizationsource potential to evacuate the ions from the first end of said vessel.4. The ionization chamber of claim 1, wherein the first ionizationsource potential is equal to the first ion gate potential.
 5. Theionization chamber of claim 1, wherein, during a release stage: saidionization source is further configured to be charged to a secondionization source potential that is greater than the first ionizationsource potential; said mid-ring electrode is further configured to becharged to a second mid-ring potential that is greater than the firstmid-ring potential; and said ion gate further configured to be chargedto a second ion gate potential that is less than the second mid-ringpotential and the second ionization source potential, wherein the secondmid-ring potential and the second ion gate potential are configured tocooperate to move a pulse of the ions through said ion gate and fromsaid second end of said vessel.
 6. The ionization chamber of claim 5,wherein, during the release stage, a difference between the secondionization source potential and the second mid-ring potential is lessthan a difference between the second mid-ring potential and the secondion gate potential.
 7. The ionization chamber of claim 1, wherein saidmid-ring electrode is further configured to be charged to a potentialgradient over an axial dimension of said mid-ring electrode.
 8. Theionization chamber of claim 7, wherein the potential gradient is axiallyasymmetrical.
 9. The ionization chamber of claim 1, wherein said iongate comprises a conductive grid disposed between the ionization regionand a drift region.
 10. A method of compressing ions, said methodcomprising: generating ions at an ionization source within an ionizationchamber; charging a mid-ring electrode to a first mid-ring potential togenerate a potential well relative to a first ionization sourcepotential and a first ion gate potential, the potential well configuredto collect the ions; and charging an ion gate to the first ion gatepotential to prevent the ions from traveling through the ion gate andinto a drift region.
 11. The method of claim 10 further comprisingcharging the ionization source to the first ionization source potential,wherein the first ionization source potential and the first ion gatepotential are greater than the first mid-ring potential.
 12. The methodof claim 11 further comprising: charging the mid-ring electrode to asecond mid-ring potential that is greater than the first mid-ringpotential; and charging the ion gate to a second ion gate potential thatis less than the second ionization source potential and the secondmid-ring potential to pulse the ions into the drift region.
 13. Themethod of claim 12, wherein the second ion gate potential is equal tothe first ion gate potential.
 14. The method of claim 12, wherein thesecond ionization source potential and the second mid-ring potential aregreater than the second ion gate potential, such that a pulse of theions travel through the ion gate.
 15. The method of claim 10, whereincharging the mid-ring electrode to the first mid-ring potentialcomprises charging the mid-ring electrode with a potential gradient overa length of the mid-ring electrode in an axial dimension of theionization chamber.
 16. An ion mobility spectrometer (IMS) device,comprising: a drift tube defining a drift region therein; and anionization chamber defining an ionization region therein, saidionization chamber comprising: an ionization source located at a firstend of said ionization region and configured to generate ions, saidionization source configured to be charged to a first ionization sourcepotential during an ion compression stage; an ion gate located adjacentto said drift tube and at a second end of said ionization region, saidion gate configured to be charged to a first ion gate potential duringthe ion compression stage; and a mid-ring electrode located between saidionization source and said ion gate, said mid-ring electrode configuredto be charged, during the ion compression stage, to a first mid-ringpotential that is less than the first ionization source potential andthe first ion gate potential, the first mid-ring potential configured togenerate a potential well, proximate said mid-ring electrode, where theions collect during the ion compression stage.
 17. The IMS device ofclaim 16, wherein, during a release stage: said ionization source isfurther configured to be charged to a second ionization source potentialthat is greater than the first ionization source potential; saidmid-ring electrode is further configured to be charged to a secondmid-ring potential that is greater than the first mid-ring potential;and said ion gate is further configured to be charged to a second iongate potential that is less than the second ionization source potentialand the second mid-ring potential, wherein the second ionization sourcepotential, the second mid-ring potential, and the second ion gatepotential are configured to cooperate to move a pulse of the ionsthrough said ion gate and into said drift region.
 18. The IMS device ofclaim 17, wherein, during the release stage, a difference between thesecond ionization source potential and the second mid-ring potential isless than a difference between the second mid-ring potential and thesecond ion gate potential.
 19. The IMS device of claim 16, wherein saidmid-ring electrode is further configured to be charged to a potentialgradient over an axial dimension of said mid-ring electrode.
 20. The IMSdevice of claim 16, wherein said ion gate is further configured to becharged to the first ion gate potential to prevent the ions fromtraveling through said ion gate and into said drift region.